What is the diagnosis for a male patient with a pituitary adenoma, presenting with reduced libido, infertility, low testosterone, low Luteinizing Hormone (LH), and low Follicle-Stimulating Hormone (FSH)?

Diagnosis: Hypogonadotropic Hypogonadism (Answer D)

This patient has hypogonadotropic hypogonadism (secondary hypogonadism) caused by his pituitary adenoma, which is compressing or disrupting normal gonadotroph function, resulting in deficient LH and FSH secretion with consequent low testosterone.

Diagnostic Reasoning

The clinical presentation provides a clear diagnostic pattern:

• Low testosterone with low (or inappropriately normal) LH and FSH defines hypogonadotropic hypogonadism, indicating a problem at the hypothalamic-pituitary level rather than the testes 1
• The presence of a pituitary adenoma explains the mechanism: mass effect from the tumor compresses normal pituitary tissue, disrupting gonadotropin secretion 1
• Central hypogonadism occurs in 36-95% of patients with nonfunctioning pituitary adenomas, making this the most common hormonal deficit after growth hormone deficiency 1

Why Other Options Are Incorrect

Primary testicular failure (Option A) would show elevated LH and FSH (hypergonadotropic hypogonadism) as the pituitary attempts to compensate for testicular dysfunction 1. This patient has the opposite pattern.

Androgen insensitivity (Option B) is a genetic disorder where testosterone levels are typically normal or elevated with elevated LH, as the body cannot respond to androgens 1. This patient has low testosterone.

Hyperprolactinemia (Option C), while common in pituitary adenomas (occurring in 25-65% of cases with nonfunctioning adenomas), would require elevated prolactin levels for diagnosis 1. The question does not indicate prolactin was measured or elevated. Additionally, hyperprolactinemia causes hypogonadotropic hypogonadism as a secondary mechanism, not as the primary diagnosis 1.

Kallmann syndrome (Option E) is a congenital form of hypogonadotropic hypogonadism associated with anosmia and developmental abnormalities 1. This patient has an acquired form due to his pituitary adenoma, presenting in adulthood.

Clinical Algorithm for Distinguishing Hypogonadism Types

When evaluating a patient with low testosterone and sexual dysfunction:

1. Measure LH and FSH levels alongside testosterone 1

   • Low or inappropriately normal LH/FSH → Hypogonadotropic hypogonadism (secondary)
   • Elevated LH/FSH → Hypergonadotropic hypogonadism (primary testicular failure)

2. If hypogonadotropic hypogonadism is confirmed, measure prolactin 1

   • Elevated prolactin suggests prolactinoma or stalk effect
   • Normal prolactin with pituitary mass suggests nonfunctioning adenoma with compression

3. Obtain pituitary imaging (MRI) if LH/FSH are low with testosterone <150 ng/dL, regardless of prolactin levels, as non-secreting adenomas may be present 1

Critical Management Considerations

Before initiating testosterone replacement, this patient requires:

• Complete anterior pituitary axis evaluation to assess for other hormone deficiencies (ACTH, TSH, growth hormone), as 37-85% of patients with nonfunctioning pituitary adenomas have multiple deficiencies 1
• Never replace thyroid hormone before confirming adequate cortisol levels, as this can precipitate life-threatening adrenal crisis 2
• Neurosurgical consultation for potential transsphenoidal resection, as surgery is often first-line treatment for symptomatic pituitary adenomas 1

If fertility is desired, testosterone therapy should be avoided as it will further suppress spermatogenesis. Instead, consider gonadotropin therapy (hCG with or without FSH) or selective estrogen receptor modulators after surgical management 1.

The diagnosis is definitively hypogonadotropic hypogonadism (Option D), representing acquired secondary hypogonadism from pituitary adenoma mass effect 1.